Temple 'G' was the largest of the Selinunte temple group and measured 113.34 by 54.05 meters along the stylobate, surpassed in size only by the Temple of Apollo near Miletus and the Temple of Artemis in Ephesus. This building, although under construction from 530 to 409 BC (the long period of construction is demonstrated by the variation of style: the east side is archaic, while the west side is classical), remained incomplete, as shown by the absence of fluting on some of the columns and by the existence of column drums of the same dimensions some ten kilometers away at Cave di Cusa, still in the process of extraction. In the massive pile of ruins it is possible to make out a peristyle of 8 x 17 columns (16.27 meters high and 3.41 meters in diameter), only one of which remains standing since it was re-erected in 1832.

The interior consisted of a prostyle pronaos with four columns, with two deep antae walls ending in pilasters and three doors leading to the large naos. The naos was divided into three aisles – the middle one was probably open to the air (hypaethros). There were two rows of ten slender columns which supported a second row of columns (the gallery) and two lateral staircases which led to the roof space. At the back of the central aisle was an adyton, separated from the walls of the naos and entirely contained within it. Inside the adyton, the torso of a wounded or dying giant was found. At the rear there was an opisthodomos in antis. Of particular interest among the ruins are some finished columns showing traces of colored stucco. Temple 'G'  was dedicated to Apollo, though recent studies indicate that it be attributed to Zeus.